Half of all human cancers carry mutations in the tumor suppressor p53. The majorities of p53 negative cancers do express full length, but mutated p53. Many of the p53 mutations found in cancers are single amino acid changes in the 200 amino acid core domain of p53. These mutations are thought to destabilize the correct p53 fold and thus lead to inactivation of the p53 tumor suppressor function. Our hypothesis is that small molecules exist that can stabilize the correct conformation in p53 cancer mutants. These molecules could therefore reactivate mutated forms of p53 in cancers. Experiments in animal models have demonstrated that restoring p53 function even in advanced tumors leads to tumor regression. Small molecules that can restore function to p53 cancer mutants are therefore predicted to significantly improve the outlook for patients carrying a p53 mutation. We propose to develop a screening platform compatible with high throughput small molecule screens (HTS) to identify compounds that reactivate p53 mutants that are frequently found in human cancers. The proposed drug screen relies on unique, cheap and very efficient yeast-based assays that allow us to screen compounds simultaneously against the 70 most commonly found p53 cancer mutants. We propose to implement fluorescence-based readouts for our yeast-based system to enable HTS. In addition we propose secondary yeast assays to confirm a specific effect of small molecules on p53 cancer mutants and to determine how many different p53 mutants are rescued by one specific small molecule. A biochemical strategy that looks at effects of the identified small molecules on thermostability of p53 is proposed to select molecules that directly improve structural integrity of p53. Lastly, adaptation of a tertiary screen is proposed that will evaluate rescue compounds in mammalian cells. The immediate goal of the proposal is to develop the framework to identify small molecules that restore function to p53 cancer mutants and use these molecules later as lead compounds to synthesize derivatives to increase their therapeutic activity. Restoring p53 function in tumors has been demonstrated to reverse tumor growth in animal models and is therefore an attractive strategy for cancer treatment. [unreadable] PUBLIC HEALTH RELEVANCE: About 50% of all human cancers carry mutations in the tumor suppressor p53. p53 negative cancers generally more resistant to current treatment strategies and alternative approaches are particularly necessary for effective treatment of these cancers. The objective of this proposal is to identify small molecules that restore function to p53 cancer mutants and to develop these molecules into therapeutics to restore p53 function in tumors. [unreadable] [unreadable] [unreadable]